Characterization of Mn 2+ doped tetramethylammoniumtetrachlorozincate single crystal using EPR and optical absorption

Abstract

Studies of fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn 2+: tetramethylammoniumtetrachlorozincate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements were done at liquid nitrogen temperature (77 K). The Mn 2+ spin Hamiltonian parameters are evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field. The values of the zero field parameters that give good fit to the observed EPR spectra are obtained. The values of different parameters are: g = 1.9834 ± 0.0002, A = (105 ± 2) × 10 −4 cm −1, B = (100 ± 2) × 10 −4 cm −1, D = (349 ± 2) × 10 −4 cm −1, E = (106 ± 2) × 10 −4 cm −1 and a = (21 ± 1) × 10 −4 cm −1. The percentage of covalency of the metal–ligand bond has also been determined. From the optical absorption study, the lattice distortion is suggested. The observed bands are assigned as transitions from the 6A 1g(S) ground state to various excited quartet levels of Mn 2+ ion in a cubic crystalline field. The electron repulsion parameters ( B and C) and crystal field parameters ( D q and α) providing a good fit to the observed optical spectra are evaluated and the values are: B = 737 cm −1, C = 2322 cm −1, D q = 670 cm −1 and α = 76 cm −1. The considerable decrease in the values of B and C parameters from free ion values ( B = 960 cm −1, C = 3325 cm −1) has indicated that there exists a fair amount of covalent bonding between the central metal ion and the ligand. On the basis of deviations Δ g = g − 2.0023 it has been ascertained whether electrons are transferred to or from the central ion by the action of bonding.